1. Field of the Invention
The present invention relates to a combinatorial weighing method for use with a computerized weighing apparatus of combinatorial weighing type, in which the weighed data of a plurality of weighing machines are combined to select the weighing machines which afford the optimum combination.
2. Description of the Prior Art
The combinatorial weighing type computerized weighing apparatus is designed to provide articles having a total combined weight value equal to a target weight value or closest to the target weight value by supplying the articles to respective weighing hoppers of a plurality of weighing machines, weighing the articles which have been dispensed to the weighing machines, computing combinations of the weight values obtained on the basis of the respective weight data of the weighing machines, selecting the combination of weighing machines (which will be referred to as the "optimum combination") that gives the total combined weight value equal or closest to the target weight value within preset allowable limits, and opening only the weighing hoppers of the weighing machines providing the optimum combination.
In such a computerized weighing apparatus, the weighing hoppers which have discharged the articles belonging to the optimum combination, are supplied with articles for the next weighing cycle from pool hoppers which are arranged thereabove, and then a dispersing feeder supplies articles to the emptied pool hoppers.
FIG. 1 is a block diagram of the computerized weighing apparatus described above. In this weighing apparatus, when a timing signal T is delivered from a packaging machine (not shown) to a computation control unit 5 constructed of a microcomputer and so forth, this computation control unit 5 feeds a start signal ST to a multiplexer 3 so that this multiplexer 3 introduces the weight value data X.sub.1A to X.sub.nB (at analog values) of a plurality of weighing machines 2 into an A/D converter 4. In accordance with the weight value data which have been converted into digital values and fed to the computation control unit 5, this unit 5 computes combinations of the weight value data on the basis of preformed combination patterns. The computation control unit 5 compares the computed combinatorial weight values with the target weight value, which has been set by a target weight setting unit 7, to select the optimum combination of weighing machines until it feeds operation signals to a drive unit 1 for driving the hoppers of the weighing machines providing the optimum combination. At this time, the weight values to be selected for the optimum combination are smaller than the upper limit which is preset by an upper limit setting unit 6.
The relationship between the weighing hoppers belonging to the weighing machines and the pool hopper for supplying weighing hoppers with articles will be described with reference to FIGS. 2(a), (b) and (c). In the construction shown in FIG. 2(a), an A-side weighing hopper and a B-side weighing hopper are arranged below the A and B-side gates, respectively, of a two-gate pool hopper, so that the A-side hopper is supplied with the articles when the A-side gate of the pool hopper is opened. In the construction shown in FIG. 2(b), a dispersing chute is arranged below the pool hopper so that it can be pivoted to the right or left to disperse and supply the articles to the A and B-side weighing hoppers. In the construction shown in FIG. 2(c), on the other hand, a moving pool hopper is made movable to the right and left to supply articles to the A and B-side weighing hoppers.
Reverting to FIG. 1, the signals to be delivered from the computation control unit 5 to the hopper drive unit 1 are classified, in the construction of FIG. 2(a), into signals P.sub.1A to P.sub.nA for opening the A-side gates of the pool hoppers, signals P.sub.1B to P.sub.nB for opening the B-side gates of the same, and a signal q for opening the weighing hoppers. On the other hand, the weighing machines 2 are paired and arranged such that six pairs (i.e., twelve machines) W.sub.1A, W.sub.1B to W.sub.nA, W.sub.nB, for example, are equidistantly arranged in a circular or straight shape.
The weighing machine having any of the aforementioned constructions has its zero point shifted naturally by the ambient temperature or due to aging. This shift makes a zero-point adjustment necessary for correcting itself.
In the prior art, the shift of the zero point cannot be quantitatively judged as to the conditions under which the weighing machine is used and how long the machine is used. This makes it impossible to execute the zero-point adjustment rationally.
On the other hand, in the computerized weighing apparatus having two weighing hoppers arranged for each pool hopper, as shown in FIGS. 2(a), (b) or (c), the two weighing hoppers, i.e., the weighing machines 2 for affording the weight value data are arranged for each pool hopper. This enables the computerized weighing apparatus to have an advantage that the weight value data are obtained two times. However, the computerized weighing apparatus has a problem that, when two weighing machines belonging to one pair are both selected as part of the optimum combination to discharge the articles (which will be referred to as a "doubling discharge"), the succeeding articles cannot be supplied to the two corresponding weighing hoppers before the subsequent two weighing cycles. Because of this problem, the number of weighing machines to participate in the next combinatorial weighing cycle is reduced, if the number of the doubling discharge pairs of increased, so that the number of combinations is accordingly reduced, thereby to deteriorating the combinatorial weighing accuracy. If the doubling discharge is wholly prohibited in order to obviate that deterioration, the number of combinations in one weighing operation required for the computerized weighing apparatus causes a problem in that the number of weighing machines has to be increased. If one weighing machine belonging to one pair is replenished with articles after the a doubling discharge and is continuously selected for the optimum combination, such that it is selected again for the optimum combination to discharge its articles and is continuously caused to discharge its articles in the subsequent weighing cycle also, the computerized weighing apparatus also has a problem in that the restoring operation of replenishing the emptied weighing hopper with the articles is elongated. As a result, the combinatorial weighing accuracy is further deteriorated.